2016 Prius transmission fluid change

IMHO, it should be changed at least every 100K miles. Contaminate concentration builds up over time, chemical structures change through hot and cold cycling, age of fluid, to name a few. Let's face it, the OEM only cares about the car lasting past it's warranty period. That's their definition of lifetime, IMHO. Everything else attributed to their brand name is gravy.
If you do the change yourself, the cost is around $75 using OEM parts and fluid. I consider that cheap insurance every 100K miles.

Just my 2 cents......

 

Takes an hour or two. Four quarts of Toyota ATF WS and replacement washers will set you back about $50* USD. My preference is to do it around one year or 10,000 miles, but no time like the present. There's a link in my signature with some third gen tips, still relevant (on a phone turn it landscape to see signatures). Torque values are higher for the fill/drain bolts with gen 4, not sure why (see attached).

* That might be out of date, seems the price of the fluid has jumped of late.

 

Pay the premium price for the OEM fluid.
I normally would not make that recommendation BUT the ‘transmission’ in this car has motor-generators and windings.
The OEM stuff is proven to work.

The fluid is good for the life of the car WARRANTY.
Beyond that….. ???
There are issues of reputation but Toyota has already done the cost-benefit on that.

YMMV

 

The fill/drain bolts are "socket head cap screw" style, have a recessed 10mm hex pocket on the head. Don't be tempted to bust them loose with a 10mm Allen key, and even less so, a 3/8" Allen key (~9.5mm). You can get 10mm hex bit "sockets", and coupled with an extra-long-handled, swivel-head ratchet wrench it's a breeze. You need such a socket to use with a torque wrench too.

All of this is predicated on DIY approach. If you were to go into a dealership service department for this, tread cautiously. For whatever reason, dealerships may try to dissuade you from doing this, and if they do agree to do it, way overcharge. It's roughly similar in complexity/time to an oil/filter change, albeit a bit different. I used to say it shouldn't cost you over $100 USD at the dealership. Considering the Toyota ATF WS fluid price has inflated, say $125 at most.